Project Summary Sickle cell disease (SCD) in children is associated with a 250x greater risk of stroke than the general population. Moreover, children with SCD have significantly diminished IQ's, attention deficits, and impaired executive skills and visuo-spatial memory compared with age-matched controls. Stroke and subsequent neurological impairments in children with SCD are generally believed to stem from the presence of chronic anemia and perfusion abnormalities. These conditions lead to persistent increases in cerebral blood flow (CBF) in order to preserve adequate oxygen delivery to the tissue. Unfortunately, vasodilation, impaired cerebrovascular autoregulation, and limited vascular reserve leave the brain vulnerable to increased metabolic demand, and thus susceptible to infarct. The current standard for the assessment of stroke risk in pediatric SCD is transcranial Doppler ultrasound, which measures CBF in large feeding arteries. However, supplementary modalities to Doppler ultrasound are needed to quantify microvascular-level cerebral hemodynamics for improved detection of silent infarction risk, treatment monitoring, and prediction of neurocognitive outcome. This proposal will establish the feasibility of a non-invasive optical tool known as diffuse correlation spectroscopy (DCS) to assess microvascular CBF in pediatric sickle cell disease. To date, DCS has not been used in sickle cell disease; however, the technology's success in neonates, children, and adults, as well as the demonstrated need for microvascular perfusion monitoring in SCD suggest that the translation of DCS to SCD is likely to succeed. We will translate DCS to children with SCD using a complementary set of experiments, ranging from in vitro microfluidic models to in vivo murine models, to patient studies. First, we will utilize tissue-simulating phantoms embedded with complex microvascular-sized chambers to systematically develop and test novel DCS analysis algorithms that account for typical biophysical effects seen in sickle cell disease (Aim 1). Second, we will utilize a mouse model of SCD to investigate differences in baseline CBF and vascular reactivity to varying oxygen tensions (Aim 2). By demonstrating the utility of DCS to quantify CBF impairments in sickle mice, we can ultimately use DCS to non-invasively characterize cerebral responses to novel therapeutic strategies, and we can translate these results directly to the clinic since DCS can also be used in humans. Finally, we will test DCS for the first time in a cohort of pediatric SCD patients (n=10) and healthy age-matched controls (n=10) (Aim 3). Patients will be subjected to an orthostatic stress test to assess baseline CBF, response to postural manipulation, and dynamic cerebral autoregulation, i.e. the ability of the brain to maintain constant CBF in response to blood pressure changes. Upon completion of the proposed aims, we will have sufficient phantom, preclinical, and clinical data to support further studies that probe the prognostic value of longitudinal DCS measurements for prediction and prevention of stroke and adverse neurocognitive outcome in children with sickle cell disease.